LobHandler implementation for Oracle databases. Uses proprietary API
to create oracle.sql.BLOB and oracle.sql.CLOB
instances, as necessary when working with Oracle's JDBC driver.
Note that this LobHandler requires Oracle JDBC driver 9i or higher!

While most databases are able to work with DefaultLobHandler,
Oracle just accepts Blob/Clob instances created via its own proprietary
BLOB/CLOB API, and additionally doesn't accept large streams for
PreparedStatement's corresponding setter methods. Therefore, you need
to use a strategy like this LobHandler implementation.

Needs to work on a native JDBC Connection, to be able to cast it to
oracle.jdbc.OracleConnection. If you pass in Connections from a
connection pool (the usual case in a J2EE environment), you need to set an
appropriate NativeJdbcExtractor
to allow for automatical retrieval of the underlying native JDBC Connection.
LobHandler and NativeJdbcExtractor are separate concerns, therefore they
are represented by separate strategy interfaces.

Coded via reflection to avoid dependencies on Oracle classes.
Even reads in Oracle constants via reflection because of different Oracle
drivers (classes12, ojdbc14, ojdbc5, ojdbc6) having different constant values!
As this LobHandler initializes Oracle classes on instantiation, do not define
this as eager-initializing singleton if you do not want to depend on the Oracle
JAR being in the class path: use "lazy-init=true" to avoid this issue.

OracleLobHandler

setNativeJdbcExtractor

Set an appropriate NativeJdbcExtractor to be able to retrieve the underlying
native oracle.jdbc.OracleConnection. This is necessary for
DataSource-based connection pools, as those need to return wrapped JDBC
Connection handles that cannot be cast to a native Connection implementation.

Effectively, this LobHandler just invokes a single NativeJdbcExtractor
method, namely getNativeConnectionFromStatement with a
PreparedStatement argument (falling back to a
PreparedStatement.getConnection() call if no extractor is set).

A common choice is SimpleNativeJdbcExtractor, whose Connection unwrapping
(which is what OracleLobHandler needs) will work with many connection pools.
See SimpleNativeJdbcExtractor's javadoc for details.

setCache

Set whether to cache the temporary LOB in the buffer cache.
This value will be passed into BLOB/CLOB.createTemporary.

Default is true.

See Also:

oracle.sql.BLOB#createTemporary,
oracle.sql.CLOB#createTemporary

setReleaseResourcesAfterRead

public void setReleaseResourcesAfterRead(boolean releaseResources)

Set whether to agressively release any resources used by the LOB. If set to true
then you can only read the LOB values once. Any subsequent reads will fail since the resources
have been closed.

Setting this property to true can be useful when your queries generates large
temporary LOBs that occupy space in the TEMPORARY tablespace or when you want to free up any
memory allocated by the driver for the LOB reading.

getLobCreator

Create a new LobCreator instance, i.e. a session for creating BLOBs
and CLOBs. Needs to be closed after the created LOBs are not needed anymore -
typically after statement execution or transaction completion.

releaseResourcesAfterRead

If releaseResourcesAfterRead property is set to true
then this implementation calls
BLOB.close() or CLOB.close()
on any non-temporary LOBs that are open or
BLOB.freeTemporary() or CLOB.freeTemporary()
on any temporary LOBs.

This method can be overridden by sublcasses if different behavior is desired.